Cellulose film with anti-blocking properties

ABSTRACT

Disclosed is an integral film comprising a transparent polymeric substrate having a surface bearing polymeric beads, wherein the swell ratio, the size, and the laydown of the beads are selected so as to provide both a one sided static friction coefficient of not more than 0.68 and an internal haze value of not more than 0.1. The film provides an improved combination of slip and optical properties.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 10/104,450 filed onMar. 22, 2002, the entire contents of which are incorporated herein byreference.

FIELD OF THE INVENTION

This invention relates to polymeric films, which can be used asprotective layers in optical components. More specifically it refers topolymer films having good surface slip properties and good opticalproperties.

BACKGROUND OF THE INVENTION

Smooth film surfaces tend to ‘block’ or stick together when stacked orrolled. This is particularly troublesome when rolled substrates arestored at high temperatures and humidity. Anti-blocking or slip agentshave long been known to provide surface roughness to prevent adhesionbetween two sheets of what would otherwise be smooth film surfaces. Theeffect of roughening the surface is to reduce the frictional forcesbetween the surfaces of sheets or layers of the substrate. Manyinorganic and polymeric materials are known to act as good anti-blockingagents and various solutions to the problem have been proposed.Unfortunately, when particulates are added or surface roughnessincreased, generally, the film haze or light scattering properties ofthe films are also increased.

Another acceptable way to overcome blocking or high surface friction inrolled films is to utilize a variable knurling profile in the wound rollas described in U.S. Pat. No. 5,393,589. Knurling refers to theprocesses for producing a pattern of raised features on one or bothsides of a web. In variable knurling, the height of the raised featuresis varied throughout the length of the roll in a predetermined profileto allow for high knurl heights near the core where pressure damage canoccur and thinner knurl heights at the outer layers of the roll wheredistortion in the web can occur.

In coating anti-blocking agents on substrates used in optical devices,improved surface slip must be achieved without any deterioration of theoptical properties. An example of this situation would be the use ofanti-blocking layers on triacetyl cellulose (TAC) film as more fullydescribed later. TAC film is typically used as polarizer protectivelayers in the manufacture of LCD's. The fundamental lack of TAC polymerorientation combined with the low stresses of solvent casting, forms aunique polymer system for extremely isotropic LCD coversheets. Thesefundamental advantages have allowed solvent cast cellulose triacetate tocapture the vast majority of LCD coversheet applications. However, theTAC is a soft film and when produced and rolled, the smooth front andback film surfaces have a tendency to stick or block together andgenerate poor wound roll quality which leads to defects in the LCDprotective layers.

The typical method, which has been used to provide modified surfacefriction and anti-blocking properties to TAC films out in the industry,has been to incorporate fine silica particles (10-20 nm) into the castfilm. However, surface only application of the matting particle ispreferred as this minimizes the amount of material to be incorporated.Also for good optical properties as well as anti-blocking propertiespolymeric beads are often advantageous. A bead type can be chosen forthe functionality of the components, hardness (usually expressed asdegree of crosslinking), size and narrow particle size distribution. Forexample, U.S. Pat. No. 5,238,736 discloses the combination of thehardness of polymethylmethacrylate with the lubricity of long-chainhydrocarbons in microspheres produced from homopolymers of dioldi(meth)acrylates and/or copolymers with long-chain aliphatic alcoholesters of (meth)acrylic acid and/or ethylenically unsaturated comonomer.This type of bead is demonstrated to work well for smooth hard coatedlayers such as acrylic coatings on PET. The patent specifically teachesthat there is a minimum in the chain length for the dioldi(meth)acrylate in order for advantaged friction properties to beobserved and there are no teachings to describe the impact of a coatedmatte layer on the optical property requirements of films.

In the case of coating on a soft substrate such as TAC the degree ofcrosslinking in the matte beads is surprisingly not a sufficient measureof hardness to be able to provide good surface friction properties whichare important to predicting good wound roll quality. A better indicatorof good surface friction performance is the degree to which the beadswells in a coating solvent.

SUMMARY OF THE INVENTION

The invention provides an integral film comprising a transparentpolymeric substrate having a surface bearing polymeric beads, whereinthe swell ratio, the size, and the laydown of the beads are selected soas to provide both a one sided static friction coefficient of not morethan 0.68 and an internal haze value of not more than 0.1.

The invention also provides a process for making the integral film ofthe invention.

The film provides an improved combination of slip and opticalproperties.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

The following terms are defined for purposes of describing theinvention.

-   Degree of crosslinking means the weight percentage of polyfunctional    ethylenically unsaturated polymerizable monomers used to make the    polymer.-   Internal haze means the percentage of transmitted light that is    scattered due to particles in the film without contribution from    surface scattering effects.-   Isotropic polymer means a polymer that exhibits substantially the    same refractive index (within 0.02) in all directions.-   One sided static friction coefficient means the static friction    coefficient measured in the usual manner according to ASTM    designation G143-96 obtained by measuring the friction coefficient    between a film comprising a polymeric substrate having a surface    bearing polymeric beads in contact with the same substrate in its    uncoated form.-   Transparent means that the transmitted light is 93% or greater.-   Swell Ratio means the median bead diameter (based on volume    distribution) measured in methylene chloride divided by the median    diameter of the beads as made. Median diameter is defined as the    statistical average of the measured particle size distribution on a    volume basis. For further details concerning median diameter    measurement, see T. Allen, “Particle Size Measurement”, 4th Ed.,    Chapman and Hall, (1990).-   Total haze means the percentage of transmitted light that is    scattered due to a combination of surface irregularities and    particles in the film.-   Two sided static friction coefficient means the static friction    coefficient measured in the usual manner according to ASTM    designation G143-96 obtained by measuring the friction coefficient    between two films comprising a polymeric substrate having a surface    bearing polymeric beads.

The invention film is one that has a useful combination of optical andslip properties. Desired optical properties include low haze and goodlight transmittance making it suitable for use in optical devices. Thesubstrate may be any transparent polymer such as polyesters andpolyolefins. The preferred substrate layer is triacetyl cellulose (TAC),a polymeric material in which all or a predominant portion of the filmis cellulose triacetate. Any known sources or additives may be used inthe film. The average acetyl value of the TAC polymer preferably is inthe range of 50 to 70%, especially in the range of 55 to 65%. The weightaverage molecular weight preferably is in the range of 150,000 to250,000, especially 180,000 to 220,000. The polydispersity index (weightaverage divided by number average molecular weight) of cellulose acetateis typically in the range of 2 to 7, especially 2.5 to 4. Celluloseacetate may be esterified using a fatty acid such as propionic acid orbutyric acid, so long as the acetyl value satisfies the range.Otherwise, cellulose acetate may contain other cellulose esters such ascellulose propionate or cellulose butyrate so long as the acetyl valuesatisfies the range. The substrate film may contain a plasticizer orother additives.

Suitable polymeric beads used in the invention comprise, for example,acrylic resins, styrenic resins, or cellulose derivatives, such ascellulose acetate, cellulose acetate butyrate, cellulose propionate,cellulose acetate propionate, and ethyl cellulose; polyvinyl resins suchas polyvinyl chloride, copolymers of vinyl chloride and vinyl acetateand polyvinyl butyral, polyvinyl acetal, ethylene-vinyl acetatecopolymers, ethylene-vinyl alcohol copolymers, and ethylene-allylcopolymers such as ethylene-allyl alcohol copolymers, ethylene-allylacetone copolymers, ethylene-allyl benzene copolymers, ethylene-allylether copolymers, ethylene acrylic copolymers and polyoxy-methylene;polycondensation polymers, such as, polyesters, including polyethyleneterephthalate, polybutylene terephthalate, polyurethanes andpolycarbonates.

In a preferred embodiment of the invention, the polymeric beads are madefrom a styrenic or an acrylic monomer. Any suitable ethylenicallyunsaturated monomer or mixture of monomers may be used in making suchstyrenic or acrylic polymer. There may be used, for example, styreniccompounds, such as styrene, vinyl toluene, p-chlorostyrene, vinylbenzylchloride or vinyl naphthalene; or acrylic compounds, such as methylacrylate, ethyl acrylate, n-butyl acrylate, n-octyl acrylate,2-chloroethyl acrylate, phenyl acrylate, methyl-α-chloroacrylate, methylmethacrylate, ethyl methacrylate, butyl methacrylate; and mixturesthereof. In another preferred embodiment, methyl methacrylate is used.

In addition, a suitable crosslinking monomer is used in forming thepolymeric beads in order to produce the desired properties. Typicalcrosslinking monomers are aromatic divinyl compounds such asdivinylbenzene, divinylnaphthalene or derivatives thereof; diethylenecarboxylate esters and amides such as ethylene glycol dimethacrylate,diethylene glycol diacrylate, and other divinyl compounds such asdivinyl sulfide or divinyl sulfone compounds. Divinylbenzene andethylene glycol dimethacrylate are conveniently employed. Thecrosslinking monomer desirably represents at least 20 weight %, suitablyat least 35%, and typically at least 50 weight % of the monomer mix. Thedegree of crosslinking is determined by the weight % of multifunctionalcrosslinking monomer incorporated into the polymeric beads.

The polymeric beads used in this invention can be prepared, for example,by pulverizing and classification of organic compounds, by emulsion,suspension, and dispersion polymerization of organic monomers, by spraydrying of a solution containing organic compounds, or by a polymersuspension technique which consists of dissolving an organic material ina water immiscible solvent, dispersing the solution as fine liquiddroplets in aqueous solution, and removing the solvent by evaporation orother suitable techniques. The bulk, emulsion, dispersion, andsuspension polymerization procedures are well known to those skilled inthe polymer art and are taught in such textbooks as G. Odian in“Principles of Polymerization”, 2nd Ed. Wiley (1981), and W. P. Sorensonand T. W. Campbell in “Preparation Method of Polymer Chemistry”, 2nd Ed,Wiley (1968).

The surface of the polymeric beads may be covered with a layer ofcolloidal inorganic particles as described in U.S. Pat. Nos. 5,288,598;5,378,577; 5,563,226 and 5,750,378. The surface may also be covered witha layer of colloidal polymer latex particles as described in U.S. Pat.No. 5,279,934.

The polymeric beads used in this invention will usually have a mediandiameter of less than about 5.0 μm, typically from 0.15 to 1.7 μm, andgenerally in the range of 0.5 to 1.7 μm. For further details concerningmedian diameter measurement, see T. Allen, “Particle. Size Measurement”,4th Ed., Chapman and Hall, (1990).

The polymeric beads contained on the surface of the substrate will besuch that the swell ratio is less than 1.31. If the bead swells 31% ormore in methylene chloride, then the resulting film does not exhibit thecombination of surface slip and good optical properties that is requiredfor defect free optical device applications.

The bead laydown is preferably from 0.01 to 9.0 mg/m². When the mediandry diameter of the beads is at least 0.5 microns, the typical laydownrange is 0.01 to 2.5 mg/m², or conveniently, 0.1 to 1.5 mg/m². When themedian dry diameter of the beads is less than 0.5 micrometers, thetypical laydown range is 1 to 9 mg/m², or conveniently, 2 to 6 mg/m².

The invention also provides a method of forming a film having goodsurface slip/anti-blocking properties. The beads can be dispersed in apolymer solution designed to provide for good coating properties, butdoes not interfere with the functional performance of the film. Thepreferred binder of the second layer is a cellulosic polymer.

In the preferred embodiment, the polymeric substrate layer is TAC, thematrix of the polymeric layer containing the beads is also TAC, and thefilm desirably exhibits a static surface friction of less than or equalto 0.68 when tested against either itself or bare uncoated TAC film. Inaddition, the internal haze of the film must be less than 0.1. It isalso desired that the total haze be within a desirable range not morethan 0.90.

As shown in the examples, a method of applying the polymeric beadcontaining layer onto the substrate layer consisting of TAC filmcomprises applying the beads suspended in a dissolved binder in anappropriate solvent and applying the coating by various coating methods.The second polymer layer coating can either be applied to a fully curedTAC film or ‘in-line’ during the curing process of a solvent cast TACfilm. Methanol is conveniently included in the coating solution.

TAC films have found a large market in polarizing plate manufacturing.In this process, dyed and oriented polyvinyl alcohol (PVA) sheets areglued between protective layers of TAC sheet. The acetate cover layers(one or both sides) protect the active PVA layer from physical damageand environmental agents that could cause chemical degradation to thePVA, with resulting polarization efficiency loss. Many differentpolymers have been proposed as protective cover layers for the opticallyactive PVA sheet. To date, polymer extrusion has not been able toproduce coversheets with the desired low birefringence properties. Ingeneral, all current polarizer coversheets are made from solvent castTAC. Current industry specifications require LCD polarizer coversheetsto posses a birefringence of less than 5 nanometers. The advantage ofsolvent casting is the extremely low stresses exerted on the polymerfilm as solvent leaves the forming web. Solvent sheet casting contains20 to 40 percent polymer solids in a suitable solvent. The polymerchains are mobile in the solvent system and the stresses of hoppercoating are easily relaxed, on the casting surface prior to solventremoval. Low stresses result in low orientation and the accompanyingoptical anisotropy.

TAC polymers have a cellulose chain backbone with varying degrees ofacetylation. TAC can range in substitution from approximately 2.4 to 3acetyl substitution points on the cellulose backbone. Othersubstitutions on the cellulose backbone could be hydroxyl, propyl orbutyl groups. LCD coversheet is made with TAC substitution in the 2.8 to2.9 range. This degree of acetyl substitution results in optimum polymerproperties (such as clarity, physical strength, and polymer solubility.)TAC tends to be high in polymer molecular weight. This is due to theextremely large cellulose chains it is formed from. In the conversionprocess long cellulose chains are broken down in molecular weight andacetylated. Cellulose chains are helical in nature. The acetyl groupsadded in conversion to cellulose triacetate add bulky side groups to thepolymer chain. This results in a polymer system that has long helicalchains with bulky side groups. TAC cannot be thermally extruded, as itdoes not posses a melting point (it will oxidize first). Hydrogenbonding also plays a role in cellulose sheet formation. Long helicalpolymer chains, with bulky side groups, combined with rapid hydrogenbonding, results in a polymer system with very low order. TAC is thus avery good polymer for forming amorphous polymer sheet. The fundamentallack of TAC polymer orientation combined with the low stresses ofsolvent casting, forms a unique polymer system for extremely isotropicLCD coversheets. These fundamental advantages have allowed solvent castcellulose triacetate to capture the vast majority of LCD coversheetapplications. Low birefringence of protective layers is critical forclarity in liquid crystal displays. Orientation in the coversheetcounteracts the specific orientation in the polyvinyl alcohol activelayer, damaging the polarization efficiency of the complete package. LCDscreens contain two polarizers with four coversheets. Improperorientation in the coversheets will also reduce the focus and clarity ofthe resulting display. The overriding need for low retardationcoversheets has driven the industry to a universal acceptance of TACsheet.

A polarizer element of the invention comprises a polarizer having alaminate of the film of the invention. A liquid crystal imaging elementcomprising such a polarizer. An optical device of the invention containssuch a liquid crystal element.

The invention may be used in conjunction with any liquid crystal displaydevices, typical arrangements of which are described in the following.Liquid crystals (LC) are widely used for electronic displays. In thesedisplay systems, an LC layer is typically situated between a polarizerlayer and an analyzer layer and has a director exhibiting an azimuthaltwist through the layer with respect to the normal axis. The analyzer isoriented such that its absorbing axis is perpendicular to that of thepolarizer. Incident light polarized by the polarizer passes through aliquid crystal cell and is affected by the molecular orientation in theliquid crystal, which can be altered by the application of a voltageacross the cell. By employing this principle, the transmission of lightfrom an external source, including ambient light, can be controlled. Theenergy required to achieve this control is generally much less than thatrequired for the luminescent materials used in other display types suchas cathode ray tubes. Accordingly, LC technology is used for a number ofapplications, including but not limited to digital watches, calculators,portable computers, electronic games for which light weight, low powerconsumption and long operating life are important features.

Active-matrix liquid crystal displays (LCDs) use thin film transistors(TFTs) as a switching device for driving each liquid crystal pixel.These LCDs can display higher-definition images without cross talkbecause the individual liquid crystal pixels can be selectively driven.Optical mode interference (OMI) displays are liquid crystal displays,which are “normally white,” that is, light is transmitted through thedisplay layers in the off state. “Film-compensated super-twistednematic” (FSTN) LCDs are normally black, that is, light transmission isinhibited in the off state when no voltage is applied. OMI displaysreportedly have faster response times and a broader operationaltemperature range.

Ordinary light from an incandescent bulb or from the sun is randomlypolarized, that is, it includes waves that are oriented in all possibledirections. A polarizer is a dichroic material that functions to converta randomly polarized (“unpolarized”) beam of light into a polarized oneby selective removal of one of the two perpendicular plane-polarizedcomponents from the incident light beam. Linear polarizers are a keycomponent of liquid-crystal display (LCD) devices.

There are several types of high dichroic ratio polarizers possessingsufficient optical performance for use in LCD devices. These polarizersare made of thin sheets of materials that transmit one polarizationcomponent and absorb the other mutually orthogonal component (thiseffect is known as dichroism). The most commonly used plastic sheetpolarizers are composed of a thin, uniaxially-stretched polyvinylalcohol (PVA) film which aligns the PVA polymer chains in a more-or-lessparallel fashion. The aligned PVA is then doped with iodine molecules ora combination of colored dichroic dyes (see, for example, EP 0 182 632A2, Sumitomo Chemical Company, Limited) which adsorb to and becomeuniaxially oriented by the PVA to produce a highly anisotropic matrixwith a neutral gray coloration. To mechanically support the fragile PVAfilm, it is then laminated on both sides with stiff layers of triacetylcellulose (TAC), or similar support.

Contrast, color reproduction, and stable gray scale intensities areimportant quality attributes for electronic displays, which employliquid crystal technology. The primary factor limiting the contrast of aliquid crystal display is the propensity for light to “leak” throughliquid crystal elements or cell, which are in the dark or “black” pixelstate. Furthermore, the leakage and hence contrast of a liquid crystaldisplay are also dependent on the angle from which the display screen isviewed. Typically the optimum contrast is observed only within a narrowviewing angle centered about the normal incidence to the display andfalls off rapidly as the viewing angle is increased. In color displays,the leakage problem not only degrades the contrast but also causes coloror hue shifts with an associated degradation of color reproduction. Inaddition to black-state light leakage, the narrow viewing angle problemin typical twisted nematic liquid crystal displays is exacerbated by ashift in the brightness-voltage curve as a function of viewing anglebecause of the optical anisotropy of the liquid crystal material.

Another technique for improving wound roll quality that can be employed,which is particularly advantageous when used with wound rolls greaterthan 45 inches in diameter, is variably knurling the edges of the web asdescribed in U.S. Pat. No. 5,393,589. The height or compressibility ofthe edge knurls is varied along the length of the web in a predeterminedmanner. This invention also provides a process for forming a wound rollof a film of the main embodiment comprising passing the film through aprocessing cycle employing a variable knurl height.

EXAMPLES

Several beads were evaluated for properties such as Swell Diameter Ratioand refractive index. For refractive index measurements the polymerbeads were suspended in a standard series of Carguille oils that spanthe refractive index range of 1.40 to 1.70 in 0.004 steps. The bracketedindex was inferred when the bead contrast faded with optical microscopy.The refractive index for the beads ranged from 1.42 to 1.6. The diameterof the beads was determined by either Dynamic Light Scattering (DLS) orLow Angle Laser Light Scattering (LALLS). DLS was used to measure thehydrodynamic volume of the polymer beads in a very dilute suspension.This method is accurate for bead diameters on the order of 1.0micrometers or less and is preferred for bead compositions susceptibleto aggregation in methylene chloride solvent. LALLS, using a HoribaLA-920® instrument can be used to measure the effective diameter of thebeads on the order of 0.1 micrometers or greater. The bead types and theresults of the above-described tests are shown in Table 1. TABLE 1 BeadSample Identification and Properties Bead swell Bead Sample Beadcomposition* ratio Diameter ID monomer %/crosslinker % MeCl₂/water μ AMMA (50)/EGDM (50) 1 0.6 B MMA (50)/EGDM (50) 1 1.38 C MMA (50)/EGDM(50) 1 1.65 D MMA (50)/EGDM (50) 1 1.58 E none/EGDM (100) 1 0.18 Fnone/EGDM (100) 1 0.57 G none/EGDM (100) 1 0.71 H none/EGDM (100) 1 0.74I MMA (80)/EGDM (20) 1.28 1.5 J none/DVB-HP¹ (100) 1.31 1.6 K PMSQ 1.430.5 L MMA (98)/DVB-55² (2) 1.45 0.2 M MMA (98)/DVB-55² (2) 1.45 0.6*MMA = methyl methacrylateEGDM = ethylene glycol dimethacrylateDVB-HP¹ = 80% pure divinyl benzene from Dow ChemicalPMSQ = polymethylsilsesquioxane made as described in Example 3 of U.S.Pat. No. 5,9369031.DVB-55² = 55% pure divinyl benzene from Dow Chemical

Sample films with the bead types listed in Table 1 were prepared tocompare slip properties (more specifically the static friction) andoptical properties (total haze and internal haze). Coating solutionswere prepared by mixing cellulose triacetate (or cellulose diacetate forsamples 16 and 18) in acetone with a bead dispersion (˜25 Wt % solids)in either water or MeOH. Once dispersed the solutions were coated ontofully cured and dried TAC film. The dry coating laydown for thecomponents was 20 to 50 mg/m² of the cellulose triacetate and 0.09 up to8.4 mg/m² of the polymeric bead (dry weight). The coatings can be madeby any typical coating method such as roll or slot coating.

Total and Internal haze were measured with a Gardner Haze Meter, model:Haze-Gard Plus. When the Haze meter is operated in haze mode thepercentage of transmitted light that is scattered due to a combinationof surface irregularities and particles in the film base is measured.This is referred to as Total Haze. Five centimeter by five centimetersamples are cut from different areas of the coated sheet, measured andthe results are recorded as an average of at least three samples.Internal haze measures the clarity of film sheet without thecontribution of light scattering that results from the surface. Samplesare cut from the sheet and suspended in Decalin solution for hazemeasurement. The difference in haze between the sample measured in thisway referenced to a Decalin control is the internal haze of the sample.The recorded value for both Total and Internal haze is the average of atleast three samples.

Film surface friction was measured according to ASTM designation G143-96wherein one film sample is mounted on a stationary test roller andanother film sample is slid against the surface under tension. Thetension and force to slide is measured and from these measurements thecoefficient of friction can be calculated. In the case where a coatingis tested against a bare TAC film surface the results are referred to as“one sided” static friction, when the coating is tested against itselfthe results are referred to as “two sides” static friction.

The data for coated film properties are summarized in Table 2A and 2B.TABLE 2A Results for Beads ≧0.5 micrometers Internal Haze One sided Twosided bead (aim not static friction static friction Coating Bead laydownmore than @ 10 pli @ 10 pli ID Sample ID mg/m² 0.1) (aim not more than0.68)  1 comparison B 0.09 0.7 0.53  2 comparison C 0.09 0.69 0.6  3invention A 0.23 0.04 0.48 0.48  4 invention H 0.23 0.04 0.57 0.53  5invention F 0.46 0.06 0.59 0.48  6 invention A 0.46 0.01 0.5 0.48  7invention H 0.46 0.02 0.53 0.45  8 invention I 0.46 0.06 0.67 0.64  9invention C 0.7 0.01 0.53 0.47 10 invention A 0.93 0.05 0.49 0.48 11invention I 0.93 0.03 0.59 0.54 12 invention I 1.39 0.06 0.52 0.49 13comparison F 2.79 0.2 — — 14 comparison A 2.79 0.13 — — 15 comparison J0.46 0.37 0.47 0.43  16* comparison J 0.93 0.13 0.46 0.46 17 comparisonK 0.93 0.11 0.62 0.5  18* comparison K 2.79 0.12 0.49 0.54 19 comparisonM 0.93 0.12 sample broke 0.59*coating out of cellulose diacetate instead of cellulose triacetate

TABLE 2B Results for Beads <0.5 micrometers Internal Two sided Hazestatic friction Bead bead (aim not @ 10 pli Coating Sample laydown morethan (aim not more ID ID mg/m² 0.1) than 0.68) 20 comparison E 0.93 0.05sample broke 21 invention E 4.65 0.05 0.44 22 Invention E 8.36 0.04 0.4723 comparison L 0.93 0.03 sample broke 24 comparison L 4.65 0.02 samplebroke 25 comparison L 8.36 0.07 sample broke

Although all the beads tested were crosslinked, the results show thatwhen the measured swell ratio is 31% or greater the beads do not providea surface which is good in both static friction performance and inoptical quality. When the bead level coated is too low the staticfriction force is observed to be too high. When the bead level gets toohigh, too much light scattering or internal haze is observed. Theperformance window between these two limits depends on the bead size andthe bead swell. Two sided static friction is typically? lower than onesided static friction for invention.

A second set of samples were generated by coating cellulose triacetatesolution/bead dispersions ‘in-line’ during the curing of solvent casttriacetyl cellulose (TAC) film. The film was coated on both sides andthen wound into rolls. The rolls were held at 27° C. and 75% relativehumidity and then evaluated for roll quality. The comparison is betweena typical roll of untreated TAC film and films which have been coatedwith specific examples from the invention. The results are shown inTable 3. TABLE 3 Crossover from Coating Performance Results to ObservedWound Roll Quality bead Two sided Roll bead laydown Internal staticfriction Length Wound roll Quality type mg/m² Haze @ 10 pli (feet) (@ 45minutes) no beads 0.05 >1.0 web broke 3000 hard streaks, dimples anddistortions D 0.56 0.04 0.63 3000 no streaks, dimples or distortions G0.7 0.04 0.48 8600 no streaks, dimples or distortions D 1.39 0.05 0.488600 no streaks, dimples or distortions

The results show that the observed wound roll quality as characterizedby the presence or absence of hard streaks, dimples, or otherdistortions is significantly improved when an appropriate bead is coatedat an appropriate laydown as defined by the invention. The friction andanti blocking properties of the film were improved while the opticalproperties were not deteriorated. When the bead type, size and coatinglaydown were chosen such that the static friction measured in Table 2Aor 2B is less than 0.68, the corresponding wound roll quality was goodand the sheets did not block together when the roll was unwrapped.

When coatings of this type are used in the manufacture of polarizers forLCD applications, they are processed by saponification. In order for thecoating on the substrate to remain intact and continue to provide goodfriction performance, it is necessary that the layer not be degradedduring saponification. Table 4 shows the degradation (characterized by %weight loss of polymer) for the two polymeric binder types used in theseexamples. To determine degradation, the polymeric binders were tested inboth powder form and cast films. For the powder, 2.5 g of the polymerwas added to 10 mL of 2N NaOH @ 60° C. and stirred for 90 seconds. Thesamples were then filtered through a 0.2 micrometer nalgene filter,dried in a 60° C. vacuum oven for 72 hours and re-weighed. For the filmsamples the polymers were solvent cast and dried for a minimum of 48hours in a vacuum oven. The films were tared and placed in 2N NaOH @ 60°C. for 90 seconds, rinsed and dried in a 50° C. vacuum oven for 16 hoursand reweighed. TABLE 4 Percent Weight Loss of polymer in SaponificationDegree of Loss of Loss of Polymer type Acetylation powder sample filmsample Cellulose Diacetate 2.4 29.5% 4.77% Cellulose Triacetate 2.864.3% 0.27%

As shown in Table 4, the cellulose triacetate shows much lessdegradation when exposed to saponification conditions than the cellulosediacetate.

The entire contents of the patents and other publications referred to inthis specification are incorporated herein by reference.

1. An integral film comprising a transparent polymeric substrate havinga surface bearing polymeric beads, wherein the swell ratio, the size,and the laydown of the beads are selected so as to provide both a onesided static friction coefficient of not more than 0.68 and an internalhaze value of not more than 0.1.
 2. The film of claim 1 wherein thepolymeric beads are present on the substrate surface as a dispersion ina polymeric matrix.
 3. The film of claim 2 wherein the matrix is acellulose ester.
 4. The film of claim 3 wherein the matrix is acellulose triacetate.
 5. The film of claim 1 wherein the substrate is anisotropic polymer.
 6. The film of claim 5 wherein the substrate is acellulose ester.
 7. The film of claim 6 wherein the substrate is acellulose triacetate.
 8. The film of claim 1 wherein the bead makeup isselected so that the refractive index difference between the substratematerial and the bead material is not more than 0.1.
 9. The film ofclaim 1 wherein the bead makeup is selected so that the refractive indexdifference between the substrate material and the bead material is notmore than 0.05.
 10. The film of claim 1 wherein the beads comprisecrosslinked polymers.
 11. The film of claim 10 wherein the beads exhibita degree of crosslinking of at least 25%.
 12. The film of claim 1wherein the beads exhibit a volume average diameter of at least 0.5micrometers and the bead laydown is in the range of 0.01 to 2.5 mg/m².13. The film of claim 12 wherein the laydown is in the range of 0.1 to1.5 mg/m².
 14. The film of claim 12 wherein the swell ratio is less than1.31.
 15. The film of claim 1 wherein the beads exhibit a volume averagediameter less than 0.5 micrometers and the bead laydown is in the rangeof 1 to 9 mg/m².
 16. The film of claim 15 wherein the bead laydown is inthe range of 2 to 6 mg/m².
 17. The film of claim 15 wherein the swellratio is less than 1.31.
 18. The film of claim 1 wherein two surfaces ofthe substrate bear the polymeric beads.
 19. The film of claim 1 whereinthe swell ratio is less than 1.31.
 20. The film of claim 1 wherein thebead diameter is 0.5 to 1.7 micrometers.
 21. The film of claim 1 wherethe bead laydown is 0.1 to 2.5 mg/m².
 22. The film of claim 1 whereinthe two-sided static friction coefficient is not more than 0.68.
 23. Thefilm of claim 1 wherein the beads are made from a styrenic or acrylicmonomer.
 24. The film of claim 1 wherein the beads are made from anacrylic monomer.
 25. A process for preparing a film of claim 2comprising solvent coating a solution or dispersion of the matrix andthe beads onto the substrate and removing the solvent.
 26. A process forpreparing a wound roll of the film of claim 2 comprising variablyknurling the edges of the film.
 27. The process of claim 26 wherein theheight or compressibility of the edge knurls is varied along the lengthof the wound roll.
 28. The process of claim 27 wherein the height of theedge knurls is varied along the length of the wound roll.